1. Field of the Invention
The present invention relates to a charge pump circuit, and more particularly, to a charge pump circuit capable of high efficiency operation via arrangement of a charge distribution ratio.
2. Description of the Prior Art
Charge pump circuits are typically applied in driving circuits of electronic products, such as memory drivers, LCD backlight modules, and LED backlight drivers. The charge pump circuit accomplishes energy transfer and voltage conversion by using charges stored on capacitors to establish required positive or negative high output voltages, and also simultaneously provides different output voltages at various voltage levels.
Please refer to FIG. 1. FIG. 1 is a schematic diagram of a charge pump circuit 10 according to the prior art. As shown in FIG. 1, the charge pump circuit 10 includes a positive charge pump unit 102, a negative charge pump unit 104, a second stage charge pump unit 106, and a diode 108. The positive charge pump unit 102 is used for converting an input voltage VCI to a positive charge pump voltage AVDD, which is usually a multiple of the input voltage VCI. The negative charge pump unit 104 is used for converting the input voltage VCI to a negative charge pump voltage VCL which is a negative voltage and usually a negative multiple of the input voltage VCI. As shown in FIG. 1, the positive charge pump unit 102 utilizes two flying capacitors CF1 and CF2 and the negative charge pump unit 104 utilizes one flying capacitor CF3 for energy storage and transfer.
The conventional charge pump circuit 10 usually employs two-phase operation, including a first operation phase PH1 and second operation phase PH2, for the positive charge pump unit 102 and the negative charge pump unit 104. Please refer to FIG. 2 and FIG. 3. FIG. 2 and FIG. 3 are schematic diagrams of the charge pump circuit 10 shown in FIG. 1 operating in the first operation phase PH1 and the second operation phase PH2, respectively. The positive charge pump unit 102 includes flying capacitors CF1 and CF2, a reservoir capacitor CR1, and switches SW1 to SW8. The negative charge pump unit 104 includes a flying capacitor CF3, a reservoir capacitor CR2, and switches SW9 to SW12. Interconnections of the switches SW1 to SW12 are as shown in FIG. 2 and FIG. 3, and further description thereof is omitted for brevity. Please further refer to FIG. 2. During the first operation phase PH1, the switches SW1, SW2, and SW7 to SW10 are on, and the remaining switches SW3 to SW6, and SW11 to SW12 are off. In such a condition, the input voltage VCI charges the flying capacitor CF1 to cause the voltage across the flying capacitor CF1 to be the same as the input voltage VCI. The flying capacitor CF2 charges the reservoir capacitor CR2 to cause the voltage across the reservoir capacitor CR1 to be twice the input voltage VCI, such that the positive charge pump voltage AVDD is then outputted at two times the input voltage VCI. The input voltage VCI also charges the flying capacitor CF3.
Please further refer to FIG. 3. While operating in the second operation phase PH2, the switches SW3, SW4, SW5, SW6, SW11, and SW12 are on; the switches SW1, SW2, and SW7 to SW10 are off. In such a condition, the flying capacitor CF1 charges the reservoir capacitor CR1 to cause the voltage across the reservoir capacitor CR1 to be twice the input voltage VCI. The flying capacitor CF3 charges the reservoir capacitor CR2 to cause the voltage across the reservoir capacitor CR2 to be the negative input voltage VCI. The input voltage VCI charges the flying capacitor CF2 to cause the voltage across the flying capacitor CF2 to be the same as the input voltage VCI. Therefore, the charge pump circuit 10 can realize required multiplied positive or negative voltages by operating in the mentioned two operation phases PH1, PH2 in turn according to a charge pump clock CLK_Pump.
However, in practice, the positive charge pump unit 102 needs to achieve high pumping efficiency so that the prior art needs to utilize more flying capacitors for energy storage and transfer in addition to increased operation clock or enlarged size of semiconductor elements. For example, the positive charge pump unit 102 utilizes two flying capacitors (CF1, CF2), and the negative charge pump unit 104 also utilizes one flying capacitor (CF3). Therefore, this may waste manufacturing cost.